Many millions of houses and small buildings are located in hurricane or tornado areas in, for example, the United States, at high risk of damage from the strong winds of hurricanes or tornadoes. Recent studies of hurricane damage indicate that the most extensive damage to a house occurs when the roof is torn off, allowing the rain which often accompanies strong winds to ruin the contents of the house, and often allowing walls to collapse.
There is a great need for affordable retrofitting methods for reinforcement of wood roof frames. While prior art connectors of steel strip tie-down types excel as affordable connectors of roof structures to underlying walls in new construction of houses and small buildings, they are not as applicable when retrofitting existing roof frame structures. These fittings pose difficulties in retrofitting applications because an upper portion of the steel-strip tie must extend over the top of a rafter/truss and down the other side in order to ensure adequate tie-down strength by applying the restraining force mainly at the top of the roof frame, as compression across the grain, which wood withstands quite well. If the tie-down connectors are simply nailed into the side of the rafter/truss, as commonly done in the prior art, localized tensions are induced across the grain of the wood such that the rafter/truss member tends to split under high uplift conditions, which can release the connector's nails.
The over-the-top method is now widely recommended or required in the “Hurricane Belt” of the United States, even for retrofits of existing buildings. During retrofitting however, accessing the top portion of the rafter/truss requires removal and later restoration of an area of roofing and sheathing, which are laborious and costly operations, and thus tend to discourage such retrofit upgrading of the existing housing and building stock.
Prior art efforts to devise retrofits for reinforcement of roof structures have also been made. A number of United States patents as examples of such efforts are briefly discussed below.
In U.S. Pat. No. 5,257,483 (Netek) discloses some of the complications of retrofitting by installing anchor points in fascia and the wall below, allowing temporary placement of ties in the face of an impending storm. Winger, in U.S. Pat. No. 5,319,816, and several other inventors, disclose various temporary arrangements of multiple cables or nets over the roof which are anchored to the ground. Such temporary devices demand that the householder be at home through the hurricane season, ready to react to storm warnings quickly and competently.
In U.S. Pat. No. 5,311,708, Frye shows a retrofit roof tie-down method in which lag screws are installed upwardly through a steel angle into the lower edges of the rafter/trusses, a lower leg of the steel angle being lag-screwed into the underlying wall. Frye's lag screws into the narrow edge of the rafter/truss would however invite splitting and cause tension failure. Furthermore, only the screws near the junction of rafter/trusses with the top of the wall would contribute effectively, and the usual absence of a stud directly under a rafter/truss would leave Frye's wall lag screws rather ineffective.
Thompson, in U.S. Pat. No. 6,763,634, tries to resolve the retrofit problem by inserting ties down through the roofing and sheathing from above, with one strip on each side of the rafter/truss to form a saddle across it, which is able to effectively hold down the roofing and sheathing together with the rafter/truss. Thompson's ties extend down to connect to the underlying wall below. All this entails laborious and uncertain sealing of the roof penetrations, and interferes with any subsequent re-roofing job.
Therefore, there is a need for improved retrofitting methods for reinforcement of roof frames structures.